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DARTing Into Space

06.25.04

Imagine this: As a modern spacecraft slowly approaches the International Space Station (ISS), it makes small corrections to make sure it's perfectly on course. Finally, the docking connectors meet with an amazing level of precision. The hatch to the vehicle opens, and out steps -- no one. The extremely accurate rendezvous and docking was carried out completely by computer.

Image to right: An artist conception of the autonomous DART spacecraft as it approaches the MUBLCOM satellite. DART is scheduled to launch from Vandenberg Air Force Base in Ca. in October. Credit: NASAexplores

Currently, only the Russian Progress and Soyuz spacecraft feature a completely automated docking system. NASA's Space Shuttles do have a docking targeting system, but it only assists the pilot in the maneuver. However, if a NASA test project goes right an automated docking system may become standard equipment on future spacecraft.

NASA is about to test a new spacecraft called the Demonstration for Autonomous Rendezvous Technology, or DART. Building on the Kurs docking system installed on Russian spacecraft, DART could one day be used on next generation vehicles as outlined in the Vision for Space Exploration. The system could guide spacecraft carrying cargo or equipment to the ISS, or be used by robotic spacecraft for retrieving or servicing satellites in orbit. But, before the new system can be implemented on piloted spacecraft, it will have to be tested in space.

The computer-guided DART spacecraft will be equipped with an Advanced Video Guidance Sensor and a Global Positioning System (GPS) that can receive signals from other spacecraft to allow DART to move within approximately 330 feet of the target.

Once DART has reached that range, the spacecraft will use navigation data from its sensors to perform rendezvous maneuvers with the target. These sensors actually have a range of approximately 985 feet, overlapping with the GPS system.

NASA's Marshall Space Flight Center in Huntsville, Ala., is working with Orbital Sciences Corporation located in Dulles, Va. to develop the DART spacecraft. The flight demonstrator is nearly 6 feet long with a diameter of 3 feet, and weighs about 800 pounds, the same weight as large motorcycle.

Most of the DART hardware is already complete and being tested. The demonstrator is currently scheduled to fly in October. For that test, DART will be mounted on a Pegasus rocket, which is carried aloft by an airplane, and then launched into orbit.

The fourth stage of the Pegasus rocket will remain attached as an integral part of the spacecraft, allowing it to maneuver in space. Once in orbit, the DART will race to the target satellite -- the Multiple Paths, Beyond-Line-of-Site Communications (MUBLCOM) satellite, also built by Orbital Sciences -- for a rendezvous.

This satellite was chosen because it was equipped with special optical reflectors for use in this type of situation. Once DART has approached the satellite using the GPS system, the spacecraft will use its other sensors to demonstrate rendezvous operations, including approaching the target and moving around in close proximity to the satellite.

Image to left: The DART spacecraft will be equipped with an Advanced Video Guidance Sensor. This system is an updated version of equipment that was successfully tested on two Space Shuttle flights during the mid-1990s. Credit: NASAexplores

The 24-hour mission will be performed without intervention by a human controller. Afterward, the spacecraft will leave its orbit and burn up during re-entry.

While the DART spacecraft is only the first flight of the new system, the technology it demonstrates could have applications to future space systems development requiring in space assembly, services, or other autonomous rendezvous operations.